In the past, a high-reflectivity electrode made of silver or a silver alloy, aluminum or an aluminum alloy, or the like was used as the electrode material for obtaining ohmic contact between a p-side semiconductor and an n-side semiconductor in nitride semiconductor light emitting elements of the flip-chip type. Using these highly reflective materials and efficiently reflecting light produced in the light emitting layer of the light emitting element made it possible to produce very bright light emitting elements.
However, regardless of the electrode material, both a p-ohmic electrode and an n-ohmic electrode must be disposed to the inside of the p-n junction interface to prevent electrical leakage at the p-n junction interface in the formation of the electrodes, resulting in a region where the reflective material is not formed on the semiconductor layer surface.
This region in which no electrodes are formed can sometimes lead to light leakage from that area to the element junction board side, which decreases the emission output at the light emitting device surface.
Also, when a highly reflective material is used for the electrodes, a metal film is formed for the purpose of covering the highly reflective material to prevent migration (see WO 2006-43422, for example).
This metal film was formed in a larger surface area than that of the highly reflective material, but because it was a conductive film, it had to be formed to the inside of the p-n junction interface (on the highly reflective material side). Therefore, it was difficult to ensure that a region that allowed efficient reflection would extend all the way to the p-n junction interface.
Meanwhile, there is a method in which an oxide is formed in the region in which no electrodes are formed. This method involves, for example, forming a metal film composed of a plurality of layers, then forming a mask by photolithography, and etching so that just a first ohmic metal layer is not etching. After this, a heat treatment or the like is performed to oxidize just the unmasked region, and the mask is removed to produce an oxide region and a metal region (see JP 2002-190618A, for example).